In all honesty I never tried Nerfkitten specifically, but I can suggest a few general things I guess?
The Assassin Class Armor gives a considerable boost to your chance of starting the battle, which can help against the kitten.
Aside from that, the Sizzler 'Splosion spell (
sorry, this one has no pedia entry, so I can't link it, but you can find it in the Geocastellum intro quest Okay, I made an entry for it~) automatically hits the enemy, so it should be easier to use it to kill the kitten. Especially if you pair it up with the Geomancer Wizard Robes.
I hope this helps! ^^)/
< Message edited by AliceShiki -- 9/3/2019 4:34:35 >